Various filter systems have been developed to filter water and wastewater. Typical filter systems include but are not limited to upflow filters, upflow clarifiers, a downflow downflow clarifiers, bi-flow filters as well as various combinations of the aforementioned filter systems. The terms upflow filter and upflow clarifier refer to filter systems in which influent to be filtered is directed in an upward path to remove impurities. Conversely, the terms downflow filter and downflow clarifier refer to filter systems in which the influent is directed in a downward path to remove impurities. Bi-flow filters refer to filter systems in which the influent is directed in both a downward path and an upward path to remove impurities. The upflow fitters/clarifiers, downflow filters/clarifiers and bi-flow filters include one or more filter beds formed from one or more layers of filter media. The filter media may be supported by one or more layers of gavel. Alternatively, the one or more gravel layers may be replaced with a porous plate or other direct retention systems.
In a combined system, for example, an upflow fitter/clarifier followed by a downflow filter, the influent is initially directed upwardly through the upflow filter/clarifier to remove a predetermined percentage of the impurities in the influent and then directed downwardly through the downflow filter to remove the remaining impurities to within an acceptable limit. Where the filter system includes multiple downflow filters connected in series, the influent is directed downwardly through each of the downflow filters one after the other to remove impurities within an acceptable limit.
Regardless of the type of granular bed filter system and/or the type of the liquid to be filtered, it is common for the filter system to include an underdrain. The underdrain directs and receives fluids during operation of various cycles of the filter system including the filtration cycle (also referred to as a service run) and a washing cycle. The washing cycle may be performed by directing the washing fluid in a path opposite to the path of influent during the filtration cycle or the washing cycle may be performed by directing the washing fluid in the same path as the path of the influent during the filtration cycle. The washing fluids may include influent, pre-filtered water, air or other suitable gas. A key function of the underdrain is to evenly distribute the washing fluid through the filter bed during the washing cycle so that at least a significant amount of the impurities trapped in the filter can be removed. In the event that the underdrain does not evenly distribute the washing fluid through the filter bed, the filter bed will likely not be properly cleaned. At a minimum, this will cause much shorter filtration cycles and more washing cycles. This is undesirable, as the filter system typically cannot operate in the filtration cycle during a washing cycle.
There are many different types of underdrain systems currently marketed for use in water filtration. Some underdrains are used for water only backwash and some are capable of introducing air only, water only, or simultaneous liquid and air.
A common type of underdrain is the “lateral” style. This type of underdrain is typically made of injection molded or extruded plastic or extruded clay. The underdrain blocks are arranged in rows termed “laterals”. The laterals are typically spaced on approximately 12 inch centers leaving an approximately 1 inch space between the laterals. There are two common types of combined air/water lateral type underdrains. One type is configured to introduce air and water into a center compartment that directs the air and water through separate internal orifices into two adjacent, outer compartments. The air and water escape only from the two adjacent, outer compartments into the filter bed from combined air/water orifices in the two adjacent, outer compartments. The two adjacent, outer compartments form in essence dual internal laterals that extend generally the length of the single lateral. This type of system is subject to mal-distribution of one or more of the washing fluids. Specifically, the washing fluid can exit the outer compartments in an uneven manner along the length of the underdrain lateral leading to partial cleaning of the filter media. Underdrain laterals are subject to uplift forces that tend to separate the underdrain laterals from the filter floor. A common source of this uplift force is due to the upward flow of water and/or air pushing against the filter floor with a force equal and opposite to the resistance of the flow across the underdrain lateral. Should the underdrain laterals become sufficiently separated from the filter floor, the filter will become inoperable. All of the media must be removed and the underdrain repaired or completely removed. This is obviously extremely undesirable. Therefore, one aspect of a preferred embodiment of the present invention is to provide a cost effective manner of anchoring the underdrain laterals to the filter floor.